The article “An improved gallium liquid-metal ion source geometry for nanotechnology”, Van Es et al, Microelectronic Engineering 73-74, (2004); 132-138 describes an example of a liquid-metal ion source. Such a source generally comprises a tip configured in the shape of a needle formed of a core of a refractory material (tungsten, in this article) partially covered with a layer of electrically conductive material (gallium, in this article),
said needle having a portion for connection to an electrical generator for the application of an electrical potential to the needle,
said needle being adapted to be placed in an electrostatic optical system which is itself facing an electrically conductive substrate presenting a surface,
said needle being adapted to emit a charged particle, of a first polarity, from the layer of electrically conductive material, in the direction of the surface of the substrate under the effect of an electrical potential difference applied by the electrical generator between the substrate and the needle, to form said surface of the substrate,
said tip comprising moreover a reservoir comprising a reserve of the electrically conductive material forming said layer, said reservoir being in fluid communication with said layer, and a heat transfer device adapted to be connected to a heat generator (the electrical generator, in this article) and to liquefy the electrically conductive material contained in the reservoir to cause it to flow along the tip under the action of the heat generator.
The needle used in such methods is generally of coarse geometry (of the order of 0.4 millimeters in diameter). This makes it possible to generate an ion beam and/or to deposit accumulations of material of the order of about ten or a hundred nanometers in size on the substrate. The loss of material from the tip onto the substrate leads to an erosion which is compensated for by the flow of material from the reservoir, this material being kept fluid by the heat transfer device.
Moreover, the article “Atom-probe field-ion microscopy of a high intensity gallium ion source” by Culbertson and al. discloses a tip of the type described above, in which the ion emission is carried out at a temperature below the melting point of the material to be deposited. Thus it is possible to implement an ion emission from metals in the solid phase. For such tips, it is possible to obtain an almost atomic precision in forming the surface of the substrate. However, the autonomy of such sources remains relatively limited, due to the solid character of the material to be evaporated when it is present on the needle. This solid character prevents the flow of the material to the active site of the needle. As a result, a reservoir is not used for this type of tip
Moreover, Binnig and Rohrer have shown, for example in “Scanning tunnelling microscopy—from birth to adolescence”, Review of Modern Physics, vol 59, no 3, Part 1, July 1987, tunnel-effect electronic microscopes which comprise a tip connected to a generator capable of generating a potential difference between the tip and the substrate, to tear out an election at the tip. Such microscopes can determine an item of data on the surface of the substrate from the measured current flowing between the tip and the substrate.
However, each of these functions is implemented at the present time by a separate device.